Thread: Standard Reference Material for Hanging Hair Test

I don't want to speak for Gugi, but I think what he was talking about there is the difference in sharpness between shave-ready razors. (along the lines of debating which finishing hone is the best)

I think gugi was just wanting to see people debate what he meant

Well, let me speak for myself.

First on the geometry-sharpness issue

I totally disagree. How an edge LOOKS is totally qualitative, not quantitative.

Quantitative would be like: It takes X neuton meters of force to cut through a 1/16 inch standard monofilimant line. A measurable and somewhat repeatable measurment.

Qualitative is: It looks sharp. It shaves nice.

Well I guess my standard of good microscopy is a bit more demanding than yours. The following quantities are quantifiable to at least 1% and can be measured with good microscopy alone:

1. thickness of the edge
2. angle of the bevel
3. "jagedness" along the edge
4. "texture" of the bevels

These are the only factors that go into any geometric 'sharpness'. They have units of length or are dimensionless.

Your example involves something beyond sharpness. You are making a very simplistic model of the cutting process to the point that your single number of a force becomes so specific that it is nontransferable, and thus irrelevant. As you would probably guess any force is time-dependent. Then if you look at say the cutting of hair, the cutting of synthetic fiber, the cutting of a polycrystalline or monocrystalline copper wire etc. you will discover that the phenomena are vastly different (the dynamics on the level above bond-breaking) and the force that's relevant for one is irrelevant for the others.

Originally Posted by Alethephant

What gugi does say that appears totally at odds with all advice given on SRP to beginners: "When you start breaking down the process of shaving the sharpness of the razor is one of the less important factors." On the contrary, the typical advice is to get a "shave-ready" razor before starting.

The advice we give is the razor to be 'shave-ready' not 'sharp'. Yes sharpness is part of shave-ready, but not all of it.

See, that's the same problem I pointed out earlier - you just don't quite know what you're trying to measure, so you're doing the stuff that's easy and assume that's it.


So let's go to the interesting part

Originally Posted by Alethephant

So the real question isn't "If razor PASSES the FCT, that doesn't necessarily mean it's shave-ready.". The important question is the reverse: "If the razor FAILS the FCT, what does this mean about about shave-readiness?" If it means SOMETHING, then it is useful. The opposite of ALL is not NOTHING.

That's really a matter of which question you're trying to answer. If your goal is to evaluate a 'shave-ready' razor you really ought to worry about the first.

Now you don't care about that, all you care is to have a tool that evaluates non shave-ready razors. That is perfectly fine, but if you want your tool to be useful for getting razors towards shave-ready you still have to be able to to quantify progress towards that goal.
You are proposing to measure progress using "FCT". That is certainly 'something', and you must realize that beyond just being fun experiment the actual usefulness depends on how that method stacks against the currently available ones.
You won't know until you complete the experiment, but thing that is making me skeptical is that two of your razors still don't shave very well.
At the end of the day it's your time and your fun, but you're certainly taking a very inefficient approach.
I am not trying to discourage you, I'm just suggesting that you're lacking a critical component for the process and instead of focusing on fixing that, you're doing 'something' else just because it's easier.

I didn't invent this myself, I stole it from a very experienced member and I've quoted it many times in the past.
Honing a razor involves only two things
(1) learning to perform a steady and uniform stroke across the hone
(2) determining when to switch hones

A number from a "FCT" I guess is an attempt to address (2). I think it may be possible, but you have to go the other way around, first master that part, then correlate "FCT" numbers with it. And if it works you'd finally get to the 'is it worth it' part.

I think the variables in the cutting edges themselves will have so much variation, that any standard reference material for a hanging hair test will not eliminate or reduce enough of the "hair" variables to make the cutting edge variables any easier to control or measure.

You'd have to take into account frontal area, coefficients of friction (or just use an electronic surface tester), included angle, x-y-z axis moments-of-force at all points of the cut; etc... etc... Also add in the lateral forces generated by the slightest curve along the cutting edge; since many razor edges have some smile on them.

One big problem with substituting something else for a hanging hair, is the same problem that Catra has with selling their sharpness machine. i.e. the person or buyer that wants to test sharpness probably doesn't want to cut the silicon rubber that is used as Catra's test media...

The best I can do while sharpening is just use a hair that I'm familiar with.

I'm not saying it's not a good idea. It's just a bit on the complicated side for me. Of course, using a standard material that behaves consistently for the tools one is honing is very useful.

Now that I've typed out the long version: my short version is: I think if you want to test cutting a hair...just use a hair... (it's inexpensive, too)

A fascinating experiment!

My only two problems:

the filament is not hair (not that it matters if all you are interested in is the force taken to sever it),
both ends of the filament are captive.

If I grew my beard long enough to hold one end while I shave I can see the point of the filament ends both being captive, but people dont shave like that.

Also, what is the meaning of the term 'erosity' you used earlier - is it some sort of scientific term?

Regards,
Neil

[QUOTE=gugi;666896]
The advice we give is the razor to be 'shave-ready' not 'sharp'. Yes sharpness is part of shave-ready, but not all of it.[QUOTE]

I totally agree with Ivan here. There really is a difference between sharp and shave ready.

A sharp razor will cut hair. A shave ready razor will cut hair but will also feel smooth and comfortable on the skin.

All this filament tests is the sharpness: Will the razor cut this filament at X amount of pressure or not? The difficulty and the real skill in honing is getting that smooth factor as well.

I've seen Glen say a few times "Anyone can get a razor sharp, but getting it smooth is a whole different ball game." And thats something I came to realise pretty early on with my honing.

I could get a razor sharp enough to remove hair but it really wasnt comfortable on the skin. All my efforts became focussed on getting every ounce of smooth out of the blade.

Ot at least thats the excuse I've got for my raging HAD..!

The thread... http://straightrazorpalace.com/razor...ht-razors.html references a YouTube "Making DOVO Straight Razors" Youtube.com video. At the end, at 4'20", it talks about testing the razor edge with "artificial hair." And, you see someone performing a HHT with the artificial hair. Interesting!

Also...

Some of the comments above seem to require that all technical difficulties be worked out of the FCT before it is useful at all. The HHT is useful, but difficult to apply uniformly. If use of a FCT simply reduces the chaos, reduces the number of variables, it will be beneficial.

Originally Posted by LarryAndro

The thread... http://straightrazorpalace.com/razor...ht-razors.html references a YouTube "Making DOVO Straight Razors" Youtube.com video. At the end, at 4'20", it talks about testing the razor edge with "artificial hair." And, you see someone performing a HHT with the artificial hair. Interesting!

Also...

Some of the comments above seem to require that all technical difficulties be worked out of the FCT before it is useful at all. The HHT is useful, but difficult to apply uniformly. If use of a FCT simply reduces the chaos, reduces the number of variables, it will be beneficial.

Just to point out the "painfully" (pun intended) obvious with this Larry, Dovo factory edges are NOT shave ready to any of our standards
So although they pass Dovo's standard HHT it doesn't mean anything to the poor end user, other than the razor is sharp enough to cut their standard hair ... Exactly the point that most of us were making...

Originally Posted by gssixgun

Just to point out the "painfully" (pun intended) obvious with this Larry, Dovo factory edges are NOT shave ready to any of our standards
So although they pass Dovo's standard HHT it doesn't mean anything to the poor end user, other than the razor is sharp enough to cut their standard hair ... Exactly the point that most of us were making...

To some degree, this misses my point also.

I am not criticizing the points made on this thread as much as it might seem. I am only making a pragmatic statement that even with all the difficulties, it might move us forward.

There have been many conversations about whether the HHT is useful. Many well respected here have said that if administered correctly, properly calibrated, to them it is very useful. All I am saying is that FCT might move a useful, but problematic test, to a useful, but slightly less problematic test.

Sorry for making it seem more critical than meant.

So lets say we all agree on exactly what this filament should be and how thick it should be. Lets call that material X.

And lets say that we all agree that it should take 83g of pressure to cut material X in order to pass this test.

Would a razor that cuts material X at 83g of pressure be shave ready? No. And heres why.

- Material X may be thicker or thinner than an individuals hair, or indeed tougher or weaker, which means that the 83g of pressure needed is either too much or too little. The problem with honing to a standard sharpness is that we're not all standard. It would be like only producing size 9 shoes. The reason why the pro's can turn out consistently good razors is the P word: Practice!

- The razor may well be sharp enough to cut material X, but we still dont know if its smooth enough to put on the skin.

- How was this razor honed? Natural stones? Pastes? Synthetics? A mix of all three? All of these factors contribute to how the razor feels on the skin. Some of us like paste, others dont. Some of us (like me) prefer razors that have been finished on a natural stone. One mans meat is another mans poison and all that..!

To just say "cut material X at pressure Y = shave ready" is over-simplifying the honing process.

Dont get me wrong, its not rocket science, but it does take a little time to develop the feel of what a good edge is and what a good edge should be able to do, which is why we all keep blabbing on about getting a pro-honed edge and then practicing your own honing with that benchmark!